Thrombosis is a medical condition that results from the formation of a blood clot, or thrombus, within a vessel. Thrombi often develop in the valves, legs, or other lower abdomen (i.e. deep vein thrombosis), but may occur in other vessels. The clot is typically formed from a pooling of blood within a vein due to abnormally long periods of rest, e.g. when an individual is bed ridden following surgery or suffering a debilitating illness. In addition to thrombosis, atherosclerosis is another medical condition that results from the formation of a blockage in a vein. Atherosclerosis is due to the build of atheroma material along the arterial walls. Atheroma deposits can have widely varying properties, with some deposits being relatively soft and others being fibrous and/or calcified. In the latter case, the deposits are frequently referred to as plaque. Often thrombosis and atherosclerosis are both present in the veins. For example, a thrombus develops around the atherosclerotic plaque.
The formation of thrombi and build-up of plaque can lead to a stroke or embolism, which may cause serious health issues, including death. Strokes occur when the blood clot or plaque blocks an artery supplying blood to the brain, thus depriving the brain tissue of oxygen. Without oxygen, brain cells begin to die. Embolisms occur when a blood clot travels around the body and lodges itself in an organ. For example, a pulmonary embolism is a blockage of the blood supply to the lungs that causes severe hypoxia and cardiac failure.
For some blockages, surgical intervention with ultrasonic catheters may be necessary to remove the thrombus, plaque, or both from a vessel, such as when cholesterol or anti-coagulant medications are not able to reduce the blockage. Ultrasonic catheters for dissolution of blockages are described in, for example, U.S. Pat. Nos. 6,969,293 and 6,866,670. Removal of blockages with ultrasonic energy alone, however, often fails to completely disperse the blockage within the vessel. Rather, more complete dissolution often requires withdrawal of the ultrasonic catheter from the vessel and the introduction of one or more other catheters to finalize the clot dissolution procedure. The multiple catheter exchanges may be injurious to the patient because the blood vessel interior is delicate, may be weakened by disease, and is therefore susceptible to injury from movement of the catheter body within it. As such, the need to move a catheter, let alone multiple catheters, within the patient should be minimized.